The following relates to the nuclear power arts, nuclear reaction control arts, and related arts.
Pressurized water reactor (PWR) designs have certain benefits over other light water reactor designs such as boiling water reactor (BWR) designs. For example, a PWR does not include complex steam separation hardware in the upper portion of the reactor vessel. In conventional PWR designs, this has allowed the control rod assemblies (CRAs) to penetrate the reactor through the top of the pressure vessel with the control rod drive mechanism (CRDM) units mounted externally above the pressure vessel. In this arrangement, a vessel penetration passing a connecting rod occurs at the top of the pressure vessel, whereas in a BWR design such penetrations are at the bottom of the pressure vessel, and in some design even below the reactor core itself.
In some planned small modular reactor (SMR) designs, it is contemplated to improve upon the conventional reactor design by locating the entirety of the CRDM units inside the pressure vessel. See Stambaugh et al., U.S. Pub. No. 2010/0316177 A1; Desantis, U.S. Pub. No. 2011/0222640 A1; Stambaugh et al., WO 2010/144563 A1; and Thome et al., U.S. Pub. No. 2010/0316181 A1; all of which are incorporated herein by reference in their entireties. This arrangement eliminates mechanical vessel penetrations entirely, replacing them with electrical and/or hydraulic penetrations to drive the internal CRDM units. In some such SMR designs, it is further contemplated to employ a so-called “integral” PWR configuration in which the steam generators are also located inside the pressure vessel. See Thome et al., U.S. Pub. No. 2010/0316181 A1 which is incorporated herein by reference in its entirety.
An integral PWR with internal CRDM units places a substantial number of components inside the pressure vessel. The internal steam generators need to have sufficient height to controllably convert inlet feedwater to steam. The control rod system must also have substantial height: The motors of the CRDM units must be located at least the full length of the control rods above the reactor core to allow full rod retraction, and a similar clearance must be provided above the motors to accommodate the connecting rods when the control rods are fully retracted.
Thome et al., U.S. Pub. No. 2010/0316181 A1, which is incorporated herein by reference in its entirety, leverages the conventional arrangement of a central riser surrounded by a downcomer annulus to achieve a compact integral PWR configuration including internal CRDM units. The steam generators are located in the downcomer annulus, while the CRDM units are located inside the central riser. This enables substantial vertical overlap between the steam generators and the CRDM units, providing a more compact SMR design.